Electrostatographic process for preparing screen printing member

ABSTRACT

A novel method for preparing a stencil master is provided. The method comprises coating the voids of a suitable screen with a liquid but hardenable material which is impervious to a printing fluid and not dissolvable by said printing fluid and which has a viscosity and conductivity to permit removal by electrostatic attraction, contacting said screen in the absence of light with a member having an electrostatographic latent image, separating the screen and imaged member whereby the liquid is removed from the screen by electrostatic attraction in the charged areas of the image to provide voids in image configuration and hardening the liquid in the noncharged areas to form an imaged stencil master.

1451 Sept. 30, 1975 1 1 ELECTROSTATOGRAPHIC PROCESS FOR PREPARING SCREENPRINTING MEMBER John B. Wells, Savannah, NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Dec. 26, 1973 [21] Appl. No.: 427,591

[75] Inventor:

2,949,849 8/1960 Gundlach 3,445,226 3/1969 Gundlach et a1. 96/1 R X3,559,570 2/1971 Martel et a1. 96/1 R X 3,561,358 2/1971 Weigl 96/1 R X3,589,289 6/1971 Gosnell et a1... 101/170 X 3,676,215 6/1972 Gundlach96/1 LY X 3,687,072 8/1972 Pym 101/170 X 3,795,530 3/1974 Gundlach..96/1 LY X 3,801,315 4/1974 Gundlach et 96/1 LY X 3,806,354 4/1974 Amidonct al 96/1 LY X Primary ExaminerNorman G. Torchin AssistantE.\aminer.lohn R. Miller Attorney, Agent, or Firm-James J. Ralabate;James P. OSullivan; Donald M. MacKay 5 7 1 ABSTRACT A novel method forpreparing a stencil master is provided. The method comprises coating thevoids of a suitable screen with a liquid but hardenable material whichis impervious to a printing fluid and not dissolvable by said printingfluid and which has a viscosity and conductivity to permit removal byelectrostatic attraction, contacting said screen in the absence of lightwith a member having an electrostatographic latent image, separating thescreen and imaged member whereby the liquid is removed from the screenby electrostatic attraction in the charged areas of the image to providevoids in image configuration and hardening the liquid in the nonchargedareas to form an imaged stencil master.

12 Claims, No Drawings ELECTROSTATOGRAPI-IIC PROCESS FOR PREPARINGSCREEN PRINTING MEMBER BACKGROUND OF THE INVENTION In stencil printing aporous-filled sheet is opened up where it is desired to make an ink flowfor imaging; no ink can pass through unopened, blocked areas. Stencilprinting includes both screen process printing and mimeographduplicating. Stencil screens can be made by photoresists. For example,gelatin can be coated on a screen, sensitized by dichromate solution,dried, exposed and washed out to give an imaged screen. Ink can passthrough where light has not struck. In mimeograph duplicating, imagedstencils consist essentially of ink-impervious coatings cut to expose apermeable sheet that permits ink to pass through. The stencils arewrapped around a rotating drum of a duplicator. This drum is perforatedto permit ink brushed through it to pass to the stencil to image paperfed against the stencil on the drum.

In general, the processes for producing stencils are costly and timeconsuming. It is to this problem that this invention is directed.

DESCRIPTION OF THE INVENTION It has now been discovered that stencilscan be prepared rapidly by an inexpensive simple camera speed imagingprocess. More particularly, it has been found that when the voids of ascreen are filled by coating with a liquid but hardenable material whichis impervious to a printing fluid, not dissolvable by said printingfluid and which has a viscosity and conductivity to permit removal byelectrostatic attraction, the screen can be contacted in the absence oflight with a member having an electrostatographic latent image and themembers separated to cause the liquid to be removed from the screen byelectrostatic attraction in the charged areas of the image to providevoids in image configuration, and the liquid can be hardened in theremaining areas to form an imaged stencil master. Thus because thestencil is formed from a screen, it is not necessary to use etchsolutions in order to form the image but rather the liquid can beremoved from the screen to provide voids by simple electrostaticattraction. In addition, it is not necessary to form light sensitivecoatings on the screen as the image can be easily and rapidly formed ona photoconductive paper such as a conventional zinc oxide master and thescreen imaged by contacting the charged master with the screen andseparating the members to remove the liquid from the screen in imageconfiguration. Further,.the stencils can be prepared from conventionalmaterials and employed for both screen process printing and mimeographduplicating. Other benefits will be apparent from the following detaileddescription.

DETAILED DESCRIPTION OF THE INVENTION Screens which can be employed forthe printing stencil include mesh, fabric or cloth formed of anyweavable material such as silk, nylon, Dacron and the like fibers aswell as metal wires such, for example, as stainless steel. The screenwill preferably have from 100 X 100 to 250 X 250 US. mesh, althoughlarger and smaller screens can be employed.

Liquid materials suitable for filling the screen member include waxes,and a variety of natural polymerizable monomers and synthetic polymerswhich are of a low viscosity or can be made of a low viscosity. It isonly necessary that the material be sufficiently liquid when applied tothe screen such that it fills the voids, that the material can behardened such that it is impervious to the printing fluid employed andnot dissolvable by the printing fluid, and that the fluid can be removedfrom the screen by electrostatic attraction. Thus it can be appreciatedthat a large number of materials can be employed.

The liquid but hardenable material can be removed from the screen memberby capillary action even if the viscosity is high when the members arecontacted with the imaging member for a relatively long time. It ispreferred, however, that the liquid material have a sufficiently lowviscosity and resistivity that they can be quickly removed by use of anelectrostatic field. Nearly all of the materials are sufficientlyconductive as it is only necessary to have a resistivity of less than 10ohm/cm and for the few materials which are below this conductivity, acommon electrolyte such as salt can be added. Likewise, the viscosity isnot a critical parameter, it only being necessary for optimum resultsthat the liquid material and ink can be selectively removed by anelectrostatic field. In order to obtain the desired viscosity, themonomers or polymers can be dissolved in a suitable solvent in whichthey are soluble, as is well known to those skilled in the art.

The liquid materials which can be employed to fill the screen memberinclude materials which are hardenable at ambient temperature, orelevated temperature and which can be hardened or cured by cooling, air,or some form of radiant energy such as heat and ultraviolet light.Photo-hardenable polymers which can be cured by light are particularlypreferred as it is not necessary to adjust the temperature of the screenmember. The particular liquid employed will depend on the desired lifeof the screen member, the substrate to which it is to be adhered andother variables such as cost and availability.

Waxes can be employed which are solid at room temperature and can bemade liquid at elevated temperature. Representative examples include:beeswax, carnauba wax, parafin waxes and the like. Preferred waxes arethose melting below C and most preferably below 60C.

Liquid polymers which can be employed to fill the screen member includelow viscosity thermoplastics, thermosetting plastics thermosettingresins and photopolymers. Exemplary of suitable thermoplastics arepolyethylene, polypropylene, ethylene-vinyl acetate copolymers,propylene-modified polyethylene, acetals, acrylics,acrylonitrile-butadiene-styrene (ABS), polystyrene, cellulosics,shellac, chlorinated polyether, fluorochemicals, polyamides (nylons),polyimides, phenoxies, and vinyls. examplary of suitable thermosettingplastics are aminoplasts (urea-formaldehyde, melamine-formaldehyde),phenolics, epoxies, diphenyl oxide, polyurethanes, polyesters, diallylphthalates, and silicones. Exemplary of thermosetting resins are vinyl,acrylic, alkyd, polyurethane, silicone, phenolic, and epoxy resins.

Polymerizable monomers can also be employed to fill the screen member.For example, monomers such as methyl, ethyl and propyl methacrylate,styrene and pivalolactone can be employed with an initiator. Initiatorswhich can be employed to polymerize the aforesaid monomers (other thanpivalolactone) include conventional materials such as for example,benzoyl peroxide, and azo-bis(isobutyronitrile). An initiator forpivalolactone is triphenyl phosphine. A number of materials can beemployed and it is only necessary that the initiator or catalyst besoluble in the monomer or very finely dispersed.

Exemplary of suitable photopolyrners are the cinnamic resins ofpolyvinyl alcohol, cellulose, starch and the epoxy resin ofepichlorohydrin and 4,4- isopropylidenediphenol. Polymethacrylate andpolyamide coatings can also be employed when mixed with photosensitivepolymerizable materials.

The screen member can be filled by conventional means. For example, itmay be clipped in the liquid material ordraw bar coated.

The thermoplastic materials and waxes which are solid at ambienttemperature can be converted to a low viscosity by heat so as to renderthem electrostatically removable. The thermosetting polymers are liquidat ambient temperature or below their curing temperature andthe'photopolymers are liquid until cured such as by ultraviolet light.

If desired, a screen member can be prepared by filling the voids of thescreen member at elevated temperature with a wax or thermoplasticmaterial and then allowing the material to harden by cooling. When it isdesired to image the screen member, the material can be softened by heatto fluidize the material so as to permit removal in the charged areas byelectrostatic attraction.

In order to prevent the removal of the liquid material from the screennetwork (i.e. threads or lines of the screen) and from the intersticesin the nonimaged areas because of physical contact when the screen andimaging member are contacted and separated, it may be necessary that thescreen be doctored, after the voids are filled and before imaging, witha flexible doctor blade such as soft rubber, nylon or polyurethane. Inthis manner, the fluid is removed from the lands, and below the contactplane of the interstices so that when the screen is contacted with andseparated from the image member, the liquid is removed from the screenby electrostatic attraction in the charged areas of the image and notfrom the noncharged areas by physical contact. Whether or not it will berequired to doctor the screen depends upon the method of application ofthe liquid material, its consistency and affinity for the screennetwork.

The electrostatographic image can be formed by conventional means suchas xerography. By this method the image is formed on a photoreceptorimaging member such as a zinc oxide paper master or a selenium drum.Then the electrostatographic latent image on the imaged member iscontacted to the coated screen in the absence of light and the twomembers quickly separated. The contact and separation of the two memberscauses the liquid to be removed from the screen in areas correspondingto the charged areas. The liquid remaining in the noncharged areas onthe screen can then be hardened by heat, air, ultraviolet light or thelike, the particular treatment depending on the material employed as theliquid. Images of either positive or negative sense can be formed.

In addition to the photoreceptors mentioned, other conventionalphotoreceptors can be employed. Typical photoreceptors include inorganicmaterials such as cadmium sulfide, cadmium sulfoselenide, mercuricsulfide, lead oxide, lead sulfide, cadmium selenide and mixtures thereofdispersed in binder or as homogeneous layers. Typical organicphotoreceptors include pigments such as quinacridones, carboxanilides,triazines and the like. The electrostatographic latent image can betransferred directly from a photoreceptor to the screen member or it canbe first transferred to a dielectric material such as Mylar polyesterand the dielectric material contacted with the screen member. Further,the electrostatographic image can be formed without the use of aphotoconductor by applying a metal stencil over a dielectric member suchas a polyester film and the surface charged according to. the pattern inthe stencil. The charged film is contacted to the screen member,separated and the fluid hardened in the nonimage areas as describedabove.

When it is desired to make a positive image from an image which isnegative in sense, one may charge and expose a photoconductor toactivating electromagnetic radiation to provide a negative image andbias (charge) the screen to a potential which is approximately the sameas those areas of the image which are of the higher potential so thatwhen the two members are contacted and separated,-the nonimage areas aredeveloped to provide a stencil with an image which is posi tive insense. I

Typical inks and printing equipment can be employed with the stencilmaster of the invention. Typical inks include inks of the rubber oroleophilic type having the vehicle component for the ink pigmentsderived from various oleophilic materials such as aromatic and aliphatichydrocarbons, drying oil varnishes, lacquers and solvent-type resins. Anink or printing fluid should be selected which is compatible with thecoated screen member.

The imaged stencil can then be affixed to a duplicator or conventionalframe such as wood or steel, the screen placed against a receiver memberand ink pushed through the image voids and onto the receiver member byconventional means.

The following examples will serve to illustrate the invention. All partsand percentages in said examples and elsewhere in the specification andclaims are by weight unless otherwise specified.

EXAMPLE I A stencil was prepared as follows. An X 80 U.S. mesh stainlesssteel screen was heated to above 50C by means of a Will ScientificCompany heat gun and then coated with a liquid paraffin wax, M.P. 5052C(Bolar Chemical No. 1413) by dipping the screen in the melted wax. Azinc oxide photoreceptive paper (Brunning 2,000) was charged withnegative corona and exposed to a silver halide positive transparencyproducing an electrostatographic latent image positive in sense. Thecharged paper was contacted by hand to the screen in the dark, and thenseparated. The screen was then allowed to cool to room temperature toharden the wax. In roorn light, a wax positive image was found on thescreen consisting of voids or perforations in image configuration. Thescreen was then placed over a sheet of paper and an ink roller run overthe screen to force ink through the voids and the image was reproducedon the paper. The printing step was repeated several times and prints ofgood contrast were obtained.

EXAMPLE II The procedure of Example I was repeated but with thefollowing exceptions. The wax in Example I is replaced with a catalyzedbut uncured silicone elastomer gum [30 percent by weightpoly(dimethylsiloxane) in xylene sold by Dow Corning under thedesignation Silastic No. 182 for use as a release agent for paper], andthe screen doctored with a flexible blade. After imaging the screen isplaced in an oven for approximately 2 hours at 170C and the silicone gumhardened. Prints of good image contrast were obtained, employing thescreen.

Having described the present invention with reference to these specificembodiments, it is to be understood that numerous variations may be madewithout departing from the spirit of the present invention and it isintended to encompass such reasonable variations or equivalents withinits scope.

What is claimed is:

1. A method for preparing a stencil comprising providing a suitablescreen, coating the voids of said screen with a liquid materialhardenable at ambient or elevated temperature which is impervious to aprinting fluid and not dissolvable by said printing fluid and which hasa viscosity and conductivity sufficient to permit removal byelectrostatic attraction, said conductivity being less than ohm/cm,contacting said coated screen in the absence of light with a memberhaving an electrostatographic latent image separating the memberswhereby liquid is removed from the screen by electrostatic attraction inthe charged areas of the image to provide voids in image configurationand hardening the liquid in the noncharged areas to form an imagedstencil.

2. The process of claim 1 wherein the voids of the screen are coatedwith a silicone.

3. The process of claim 1 wherein the image on the image member isxerographically formed by charging a photoconductive layer and exposingsaid layer to imagewise light to form an electrostatographic latentimage.

4. The process of claim 1 wherein the image member comprises zinc oxidephotoreceptive paper.

5. The process of claim 1 wherein the screen is a metal screen.

6. The process of claim 1 wherein the screen is formed of stainlesssteel.

7. The process of claim 1 wherein the screen has a mesh size of from 60to 325 U.S. mesh.

8. The process of claim 1 wherein the screen has a mesh size of from to250 U.S. mesh.

9. A method of printing comprising providing a suitable screen, coatingthe voids of said screen with a liquid material hardenable at ambient orelevated temperature which is impervious to a printing fluid and notdissolvable by said printing fluid and which has a viscosity andconductivity sufficient to permit removal by electrostatic attraction,said conductivity being less than 10 ohm/cm, contacting said coatedscreen in the absence of light with a member having anelectrostatographic latent image, separating the members whereby theliquid is removed from the screen by electrostatic attraction in thecharged areas of the image to provide voids in image configuration andhardening the liquid in the nonimaged areas to form an imaged stencil,contacting the resultant stencil with an image receiving member andpassing ink through said voids to thereby form an inked image on saidreceiving member.

10. The method of claim 1 wherein the screen is coated with the liquidmaterial, and doctored with a flexible blade to remove the liquid fromthe contact plane so that when the screen is contacted with andseparated from the image member, the liquid is removed from the screenonly by electrostatic attraction.

11. The method of claim 1 wherein the electrostatographic latent imagemember contains an image which is negative in sense and the screen isbiased to a potential which is approximately the same as those areas ofthe image member which are of the higher potential so that when themembers are contacted and separated, an image is provided which ispositive in sense.

12. The method of claim 9 wherein the screen is coated with the liquidmaterial, and doctored with a flexible blade to remove the liquid fromthe contact plane so that when the screen is contacted with andseparated from the image member, the liquid is removed from the screenonly by electrostatic attraction.

1. A METHOD FOR PREPARING A STENCIL COMPRISING PROVIDING A SUITABLESCREEN, COATING THE VOIDS OF SAID SCREEN WITH A LIQUID MATERIALHARDENABLE AT AMBIENT OR ELEVATED TEMPERATURE WHICH IS IMPERVIOUS TO APRINTING FLUID AND NOT DISSOLVABLE BY SAID PRINTING FLUID AND WHICH HASA VISCOSITY AND CONDUCTIVITY SUFFICIENT TO PERMIT REMOVAL BYELECTROSTATIC ATTRACTION, SAID CONDUCTIVITY BEING LESS THAN 10**13OHM/CM, CONTACTING SAID COATED SCREEN IN THE ABSENCE OF LIGHT WITH AMEMBER HAVING AN ELECTROSTATOGRAPHIC LATENT IMAGE SEPARATING THE MEMBERSWHEREBY LIQUID IS REMOVED FROM THE SCREEN BY ELECTROSTATIC ATTRACTION INTHE CHARGED AREAS OF THE IMAGE TO PROVIDE VOIDS IN IMAGE CONFIGURATIONAND HARDENING THE LIQUID IN THE NONCHARGED AREAS TO FORM AN IMAGEDSTENCIL.
 2. The process of claim 1 wherein the voids of the screen arecoated with a silicone.
 3. The process of claim 1 wherein the image onthe image member is xerographically formed by charging a photoconductivelayer and exposing said layer to imagewise light to form anelectrostatographic latent image.
 4. The process of claim 1 wherein theimage member comprises zinc oxide photoreceptive paper.
 5. The processof claim 1 wherein the screen is a metal screen.
 6. The process of claim1 wherein the screen is formed of stainless steel.
 7. The process ofclaim 1 wherein the screen has a mesh size of from 60 to 325 U.S. mesh.8. The process of claim 1 wherein the screen has a mesh size of from 100to 250 U.S. mesh.
 9. A method of printing comprising providing asuitable screen, coating the voids of said screen with a liquid materialhardenable at ambient or elevated temperature which is impervious to aprinting fluid and not dissolvable by said printing fluid and which hasa viscosity and conductivity sufficient to permit removal byelectrostatic attraction, said conductivity being less than 1013 ohm/cm,contacting said coated screen in the absence of light with a memberhaving an electrostatographic latent image, separating the memberswhereby the liquid is removed from the screen by electrostaticattraction in the charged areas of the image to provide voids in imageconfiguration and hardening the liquid in the nonimaged areas to form animaged stencil, contacting the resultant stencil with an image receivingmember and passing ink through said voids to thereby form an inked imageon said receiving member.
 10. The method of claim 1 wherein the screenis coated with the liquid material, and doctored with a flexible bladeto remove the liquid from the contact plane so that when the screen iscontacted with and separated from the image member, the liquid isremoved from the screen only by electrostatic attraction.
 11. The methodof claim 1 wherein the electrostatographic latent image member containsan image which is negative in sense and the screen is biased to apotential which is approximately the same as those areas of the imagemember which are of the higher potential so that when the members arecontacted and separated, an image is provided which is positive insense.
 12. The method of claim 9 wherein the screen is coated with theliquid material, and doctored with a flexible blade to remove the liquidfrom the contact plane so that when the screen is contacted with andseparated from the image member, the liquid is removed from the screenonly by electrostatic attraction.